1. Field of the Invention
This invention relates to liquid crystalline cinnamic acid esters, and more particularly to liquid crystalline p-cyanocinnamic acid p'-n-alkoxyphenyl esters and nematic liquid crystal compositions containing the same.
2. Description of the Prior Art
Nematic liquid crystal compounds of nematic liquid crystal compositions have recently come into wide use in display devices and light attentuators in electronic and optical instruments because of their useful physical and chemical characteristics. Nematic liquid crystal compounds and compositions can be divided into two groups according to their dielectric anisotropy. Falling in one group are the Nn-liquid crystal compounds or Nn-liquid crystal compositions which have negative dielectric anisotropy, and falling in the other are the Np-liquid crystal compounds or Np-liquid crystal compositions which have positive dielectric anisotropy.
As is well known in the art, nematic liquid crystal compounds and compositions are used in electro-optical display elements in which the optical appearance thereof is changed by application and removal of an electric field. One example of a liquid crystal display element is the DSM (Dynamic Scattering Mode) type display element, and another example thereof is the FEM (Field Effect Mode) type display element.
From the viewpoint of practical use, nematic liquid crystal compound or composition is preferably in the mesomorphic state over a wide temperature range, particularly one which covers low temperatures.